1. Field of the Invention
This invention relates generally to whipstocks, and more particularly to a millout whipstock apparatus and method wherein the whipstock is lowered on a drill string, secured inside the casing by slips, and then cemented in place inside the casing to laterally deflect a motorized side cutter mill assembly for cutting a window in the casing.
2. Brief Description of the Prior Art
In the drilling of wells, such as oil and gas wells, wherein casing is set in the well bore, obstructions and blockages are often encountered which interfere with the production or further drilling of the well. In such cases, it is sometimes necessary or desirable to deflect the drilling tool angularly to pass around the blockage or obstruction, and reorient the hole. This is usually accomplished by installing a "whipstock" in the casing which is a guide element having a longitudinally tapered, upwardly facing, arcuate face or deflecting surface. A casing mill is then run down inside the casing and when it contacts the deflecting surface, the mill is deflected laterally at an angle to cut a hole or window through the side wall of the casing so that drilling may be continued through a new bore which is directed downwardly and laterally.
Special anchoring systems and packers have been employed for mounting the whipstock in the casing. There are several patents which disclose various whipstock anchoring systems and packers.
Cagle et al, U.S. Pat. No. 3,908,759 discloses a whipstock installation wherein a modified bridge plug having a splined latch-up device at its upper end is first set by wireline in the casing. A starter drill bit at the bottom of the drill string is connected to the top end of a whipstock by a shear pin and the whipstock has a mating splined latch-up device at its bottom end. The whipstock is lowered to connect it to the bridge plug. The splined latch-up prevents the whipstock from turning or moving up the hole. The starter drill bit is released by the weight of the drill string shearing the shear pin, and when released, the starter drill bit mills a window through the casing. The starter drill bit is then replaced by a larger diamond drill bit.
Szescila, U.S. Pat. No. 4,153,109 discloses a whipstock installation wherein a bridge plug or packer having slips and an orienting device is first run downhole on a setting tool. The slips are set hydraulically by a tandem cylinder and piston arrangement. The setting tool is removed, and then the whipstock connected by a shear bolt on another setting tool is run downhole and anchored to the bridge plug or packer and the bolt is sheared by an upward pull. A drill bit is then lowered downhole to mill a window through the casing.
Brock, U.S. Pat. No. 4,266,621 discloses a milling cutter which is used with a whipstock. The whipstock is landed on a cement plug and has a slip type anchor means which grip the casing. No details of the anchor means or method are discussed or shown. To enhance the cutting action, the milling cutter is structured such that the bit cannot rotate in a dead center position.
Holland et al, U.S. Pat. Nos. 4,285,399 and 4,304,299 disclose a whipstock installation wherein a bridge plug or packer having slips and orienting keys is run downhole on a setting tool. The slips are set by opposing upward and downward forces, or hydraulically. The setting tool is removed, and a surveying instrument is lowered to determine the orientation of the keys. Then the whipstock is run down and anchored to the bridge plug or packer. A drill bit is then lowered downhole to mill a window through the casing.
McLamore, U.S. Pat. No. 4,397,355 discloses a whipstock setting apparatus which includes a whipstock having an anchor packer connected on its lower end and a cutter assembly connected at its upper end. The assembly has a fluid line connecting the bore of the cutter to the anchor packer for setting the packer. The assembly is lowered as a unit on the drill string and set by pressuring the drill string without having to make a round trip. The packer has opposed slips which are set by pressuring the drill string which opens a check valve and moves a piston/mandrel downward to expand the slips. The drill string and cutter are released by rotating the string to shear the connection with the whipstock which also severs the fluid line and the cutter mills a window through the casing. When the fluid line is severed, the check valve closes to maintain pressure in the packer and the vertically opposed slips prevent longitudinal movement of the whipstock.
Bailey et al, U.S. Pat. No. 4,765,404 discloses a whipstock setting method and apparatus which includes a whipstock having a packer connected on its lower end and a cutter assembly connected at its upper end. The assembly has a fluid line connecting the bore of the cutter to the anchor packer for setting the packer. The assembly is lowered as a unit on the drill string and set by pressuring the drill string without having to make a round trip. The packer has opposed slips which are set by pressuring the drill string which moves a piston/mandrel downward to expand the slips and has a lock nut which interacts with the mandrel to maintain the set position of the slips. The drill string and cutter are released by rotating the string to shear the connection with the whipstock which also severs the fluid line and the cutter mills a window through the casing. When the fluid line is severed, the lock nut maintains compression on the packing assembly and the vertically opposed slips prevent longitudinal movement of the whipstock.
The present invention is distinguished over the prior art in general, and these patents in particular by a millout whipstock having a cylindrical body with a stabbing nose at the bottom and an angular deflection shoe at the top. A drill string extends through the deflection shoe and is connected to a pressure housing keyed in a slotted torque key housing secured in the body. A piston housing is secured in the body beneath the pressure housing. A piston mounted in the piston housing has an upper portion extending through the pressure housing and is pinned in a raised position by shear pins. A slip expander having angled outer surfaces is connected to the bottom of the piston. Slips supported adjacent openings in the side wall of the body have an angled slot engageable with the expander angled surfaces. A fluid path extends through the drill string, pressure housing, piston housing, and piston, and is closed off by a rupture disk. The body is lowered by the drill string onto a cement plug in the casing. The slips are set by applying fluid pressure in the drill string to shear the shear pins and force the piston and expander downward to wedge the slips outward to grip the casing interior. The body is cemented in the casing by pumping cement down the drill string which bursts the rupture disk and flows to the exterior of the piston and through the bottom of the body filling the space around the stabbing nose and the interior of the body surrounding the expander assembly and lower portion of the piston. The drill string is then removed and a window is cut through the side of the casing by a mill.